EM78P510N
8-Bit Microcontrollers
6.7 Power-on Considerations
Any microcontroller is not warranted to start operating properly before the power supply
stabilizes in steady state. The EM78P510N has a built-in Power-on Reset (POR) with
detection level range of 1.9V to 2.1V. The circuitry eliminates the extra external reset
circuit. It will work well if Vdd rises quickly enough (50 ms or less). However, under
critical applications, extra devices are still required to assist in solving power-on
problems.
6.7.1 External Power-on Reset Circuit
The circuit shown in Fig.6-12 implements an external RC to produce a reset pulse. The
pulse width (time constant) should be kept long enough to allow Vdd to reach minimum
operation voltage. This circuit is used when the power supply has a slow rise time.
Because the current leakage from the /RESET pin is about ±5μA, it is recommended
that R should not be greater than 40K. In this way, the voltage at Pin /RESET is held
below 0.2V. The diode (D) acts as a short circuit at power-down. The capacitor, C, is
discharged rapidly and fully. Rin, the current-limited resistor, prevents high current
discharge or ESD (electrostatic discharge) from flowing into Pin /RESET.
VDD
/RESET
R
C
D
Rin
Fig. 6-12 External Power-on Reset Circuit
56 •
Product Specification (V0.9) 09.12.2006
(This specification is subject to change without further notice)
ELAN [ ELAN MICROELECTRONICS CORP ]
